1. Technical Field
The present disclosure relates to systems and methods for automatic shut down and restart of an internal combustion engine to enhance vehicle launch performance.
2. Background Art
An assisted direct start (ADS) engine may use a number of factors to determine when to shut down and restart the engine to achieve the goal of reducing fuel consumption and emissions while the vehicle is stationary. Typically, the engine is shut down when wheel speed is zero and the brake pedal is depressed (for automatic transmissions), or the transmission is in neutral and the clutch pedal is depressed (for manual transmissions). Other considerations may include the engine coolant temperature, battery state of charge, fuel rail pressure, A/C operation, and others that may be used to prevent an engine shut down and/or to initiate an engine restart. Physical limits of the ADS system associated with engine/transmission inertia, starter design, combustion control limits, etc., may also impose constraints on the time required to shut down and restart the engine. This time may adversely impact vehicle launch performance after an engine shutdown, particular in vehicles with an automatic transmission. As such, it is desirable in some cases to avoid shutting the engine off, or to restart the engine in anticipation of a vehicle launch to improve launch performance.
Prior art strategies may restart the engine when the accelerator pedal is depressed, but the engine start delay and resulting launch performance may be unacceptable for various situations. More complex systems include the use of a vehicle mounted camera to detect traffic signal changes, or a wireless receiver that receives a signal from an intelligent traffic control device to determine when to restart the engine.